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International Archives of the Photogrammetry, Remote Sensin g and Spatial Information Sciences, Vol XXXV, Part B2. Istanbul 2004 
  
data to Base Image Recording, which records them 
on disk arrays. 
At the end of the contact with the satellite, the 
serial data stored on the disk arrays are converted 
into image files that are recorded on tapes and 
telemetry files that are processed to create support 
data elements that are stored in the database. 
GPS Constellation 
ue uei mo e Ar rein CL 
GPS Link 
= 
Wideband Downlink 
   
Narrowband Uplink 
(Primary Frequency) 
     
Narrowband Uplink — 
  
  
  
  
  
(Backup Frequency) yn (320 Mbps) 
Data Type 
WBDL Image 
Narrowban m are 
Downlink Metadata 
NBDI. Tasking 
Response 
NBUL asking 
Instructions 
  
  
  
  
Figure 2 . Uplink and Downlink 
3 Hours before the pass an optimization is 
performed for to be collected candidate image 
regions by running the mission planning software 
after which the collection plan is saved by 
considering the weather forecast which is received 
from weather forecast data provider company via 
ftp. 
2.4. Contact with IKONOS 
2.4.1. Realtime mode : 
10 minutes prior to contact ground station 
equipment connected to the antenna are switched 
to the real time mode. 3.5 minutes prior to contact 
the antenna points to the location where the 
satellite is expected to appear above the horizon in 
program track mode. Upon contact satellite 
authentication commands and collection plan are 
sent within a 25 second window to the satellite. 
At the start of the activity window, the ground 
station RFT receives a narrowband (NB) signal 
from the satellite. The ground station RFT is also 
transmitting a NB to the satellite. If the high 
powered amplifier (HPA) on the RFT is not active, 
the satellite will not receive the signal. The 
command status indicator goes from “Unlocked” 
to "Locked" It indicates that the satellite's receiver 
is "locked" onto the signal transmitted by the 
ground station. Once the operator has verified that 
681 
the NB receiver on the satellite is working, the 
ground station signal must be modulated and the 
crypto signal and command sequence should be 
sent to the satellite within 25 seconds. The satellite 
maneuvering to the imaging place after onboard 
software execute the tasking package, this 
maneuvers called as slew maneuvers of the 
satellite and the satellite cannot take any image 
during that time since the actuators is returning the 
satellite exact imaging place. 
2.4.2. How to Satellite Process Collection : 
Onboard software receives the commands and 
processes them.Then it calculates the scan and 
slew durations for an image region.Scan is the 
actual collection time for an image region ,slew is 
the waste time between the image regions. 
Actually the satellite collects an image region 
then it returns another image region so we called 
this duration as slew. 
While the satellite is collecting the image regions, 
Image Data is sent to ground in realtime over a 
320 Mbit/Sec link. This image data is saved along 
with the metadata which is used for rough 
coordinate assessment. Then the browse image is 
subjected to cloud cover assesment. 24 hours later 
the real satellite attitude information is sent from 
(POC) and it is processed to have accurate 
coordinate information for the image regions. 
3 TOOLS FOR IMAGERY COLLECTION 
3.1. Cloud Forecast 
After getting 4 days cloud forecast information for 
the whole communication cone from the 
meteorological service provider the relevant 
satellite pass is either requested, modified or 
canceled from Primary Operations Center (POC) 
depending on cloud cover. As you can see from 
the Figure 3 Cloud Forecast Information, the 
Cloud Cover data is sent by the national 
meteorological institute for four days forth. The 
display has grid lines with 10 degree and at the top 
of the image there is a legend for the cloud 
predictions information. Left column is related 
with the prediction start time which is calculated 
by the agency with compound several 
meteorological data into the calculations and then 
the software does some calculations with iterations 
of the mathematical models. The right column has 
this iteration for the related days cloud cover 
information. For example the software was run on 
Wednesday 13 August for the 18 August 2003